This invention relates to structures for supporting turbines, and more specifically for the support of turbines arranged to be immersed in a water current and driven by the kinetic energy of the flow of water.
In our British Patents GB 2256011 B, GB 2311566 B and GB 2348250 B we have disclosed constructions pertaining to water driveable turbines; i.e. rotors supported within the water column of the sea, river or an estuary so that the flow of water may turn the rotor to produce either electricity or shaft power for utilisation for a required purpose.
When a turbine is used in such a way that it is driven by a flow of water the extraction of energy from the flow causes reduction in momentum of the passing water which in turn causes large reaction forces on the turbine which manifest themselves primarily as a thrust force acting in the direction of the flow and proportional to the numerical square of the mean velocity through the rotor. This phenomenon is a consequence of the laws of physics and will occur regardless of the turbine rotor design. In all cases the thrust on the rotor will be in direct proportion to the product of the square of the mean velocity of flow through the rotor and of the swept area of the rotor.
In general, the more powerful and efficient the turbine rotor, the greater the forces that need to be resisted, although under certain conditions such as “run away” large thrust forces can be produced even when the turbine is not delivering much, or any, usable power to the shaft. This is of course a direct consequence of the fact that the forces needed to hold the rotor in position are the reaction to the forces transmitted to the turbine rotor in order to rotate it, which in turn give a measure of its efficacy for the generation of shaft power.
Therefore an essential requirement for any such turbine is for the rotor which extracts the energy to be held in position by a structure with adequate reserves of strength to resist the static and also the dynamic forces imposed on the rotor not only by the effect of extracting energy from the flow, but also from other effects that may in some cases apply, such as passing waves, runaway conditions or unusual loads applied during installation or recovery of the turbine or other components.
Provision of such a structure is complicated by a number of other general requirements, namely:                the structure shall not unduly interfere with the flow of the water through the rotor due to the effect of the wake it will develop (or it would reduce the efficiency of the rotor),        the structure should also be as economical to manufacture as possible in order to minimise the costs of the system,        there needs to be some practical and cost-effective method for installing the structure in a location with strong currents        there needs to be some practical and cost-effective-method for installing the turbine rotor or rotors on the structure and then for gaining access to the rotor or rotors in order to maintain and when necessary to replace or repair them.        